1. Field of the Invention
This invention relates to the binding straps used for tightly binding wires, pouches etc. and is particularly concerned with the improvement of the binding straps mostly used for binding electric cables.
2. Description of the Prior Art
Binding straps made of metal or synthetic resin generally used for the abovementioned purposes and synthetic resin binding straps made of nylon, polyethylene etc. are in general use except for large or especially heavy articles. Synthetic resin straps are characterized in that they are quite easy to manufacture, suitable for mass production, and easily made into various kinds of shape. In particular, nylon binding straps have recently been used for binding electric cables in the fields of computors, automatic control electric apparatus, motorcars and others, since they are excellent in electric characteristics as well as in strength and formability. This invention relates to the improvement of binding straps which are entirely formed in one body with synthetic resin.
Binding straps have to present various characteristics and it is positively necessary for them to be easy to handle and to bind up and excellent in binding strength. Generally, handling is mutually contradictory to binding strength, that is, the easier to handle the strap structure is, the lower the binding strength thereof becomes. Accordingly, laborious researches have been conducted in order to obtain the binding straps with possess both advantages, but sufficient straps have not been brought about so far.
FIG. 12 shows an example of a head portion of a conventional binding strap. A strap body 31 extends from the side of the head portion 30 and a tongue 34 is connected to a base portion 35 toward inner side 33 of a strap body insertion hole 32 formed at the center of the head portion 30.
When the above binding strap is used to tie up electric cables 40 etc. as shown in FIG. 1, the strap body 31 is adapted to encircle the cables 40 and the forward end thereof is inserted through the hole 32 and pulled. Then, the strap body 31 is fastened to the head portion 30 with the engagement of saw blade teeth 36 provided on the strap body 31 with saw blade teeth 37 provided on the tongue 34.
As seen from FIG. 12, since the tongue 34 bends about the base portion 35 as a fulcrum, it moves in the direction of arrow A when the strap body 31 is inserted in the direction of arrow C through the hole 32. Tongue 34 moves in the direction of arrow B when tension acts in the direction of arrow D on the strap body 31. Therefore, it is necessary to decrease the strength of the base portion 35 to facilitate the insertion of the strap body 31 through the insertion hole 32. However, the strength of the base portion 35 must not be decreased beyond a certain limit, because the force of the tongue 34 pressing the strap body 31 will become to small. Besides, the simultaneous engagement of a number of teeth 36 with teeth 37 cannot be assured if the tongue 34 is too flexible. In order to engage a number of eeth 36 with teeth 37 simultaneously, the teeth 36 must correspond accurately and closely to the teeth 37. However, in the strap as shown in FIG. 12, the teeth engagement is not sufficient since the tongue moves in the direction of arrow A - B in FIG. 12.
Another prior art strap such as in U.S. Pat. No. 3,588,962 includes the binding strap wherein the base portion of the tongue is made narrower to make it easier to bend a tongue 34. The strap of this type has drawbacks in that the metal mold for molding the binding straps is too complicated, with the result that productivity is astonishingly lowered and sufficient binding strength cannot be obtained since such strength is attributable to the strength of the base portion of the tongue. As desired above, in prior art devices the binding straps with a structure which facilitated handling had drawbacks in that the binding strength was weakened and formability became worse.